This invention relates generally to semiconductor structures and devices and to a method for their fabrication, and more specifically to methods of removing silicon oxide from a surface of a substrate.
Semiconductor materials such as silicon typically form a native oxide when exposed to an oxygen containing environment such as ambient air. Often, it is desirable to remove the silicon oxide from a surface of a semiconductor surface before depositing or growing layers on the surface during the manufacture of semiconductor devices. By way of particular example, native oxides are desirably removed from a surface of a silicon wafer prior to growing epitaxial layers on the silicon wafer.
Typical silicon oxide removal processes include wet or dry etches, such as hydrofluoric or buffered hydrofluoric etch processes, or high temperature heating of the surface (e.g., heating the silicon surface to more than 1000xc2x0 C.). While methods including hydrofluoric or high-temperature techniques are suitable for removing silicon oxide in some instances, such processes may be undesirable for some applications. In particular, hydrofluoric etch processes arc generally undesirable when an oxide-free surface is desired for subsequent epitaxial growth or deposition of material on the oxide-free surface, because, in part, hydrofluoric etch processes often result in damaged and/or disordered silicon surfaces. In this case, the surface must be exposed to an anneal process, typically having a temperature greater than about 1000xc2x0 C. Similarly, high-temperature oxide removal processes are generally undesirable after the semiconductor wafer has undergone other processing such as diffusion, implantation, or material deposition, because the requisite high temperature may cause unwanted diffusion of materials within the semiconductor structures. In addition, heating wafers, particularly wafers having a diameter of about 200 mm or more, to a temperature of about 1000xc2x0 C. is relatively difficult and will create a lot of undesired stress in the wafers. Although it is also possible to use thermal de-oxidation at a relatively low temperature of about 900xc2x0 C., complete removal of SiOx from surface is very difficult and requires a long time cycle. Accordingly, improved methods for removing silicon oxide from a surface of a semiconductor are desired.